Diagnostic imaging methods include devices utilizing a variety of techniques such as X-ray, CT, ultrasonic, RI imaging, or MRI. Among them, MRI is the least harmful to the human body as compared with the other diagnostic imaging methods and forms images of the constituents in the human body. Hence, MRI is a very important device in clinical practice.
MRI devices can obtain tissue parameters such as spin density, T1, T2, chemical shift, magnetic transition, chemical exchange saturation transfer, blood flow, or spectroscopy, which are unique information of the living body. Various biometric information images can also be obtained through such parameters.
Magnetic Resonance Angiography (MRA) is a method for measuring a blood flow in the arteries and veins of the human body using the MRI device and reconstituting the measured blood flow as an image. The MRA is currently providing clinical information which is very important for the diagnosis and treatment of vascular diseases. In the case of MRA imaging, there are various methods that utilize the properties of the blood flow rate, (i.e., TOF (time of flight)), using T1-weighted imaging of the blood flow.
FIG. 1 represents a pulse sequence of FLASH (Fast Low Angle Shot) used to obtain a conventional MRA image. FIGS. 2a to 2c represent images acquired using a FLASH pulse sequence, which show images of an artery, vein, and artery & vein.
FLASH techniques have advantages such as a rapid image acquisition speed, short TE (echo time) and TR (repetition time), and low flip angle, but they have disadvantages as compared with spin echo imaging techniques; for example, the contrast of the tissue is lower, many artifacts are generated, and the signal-to-noise ratio (SNR) is low.
Further, T2* relaxation represents a traverse attenuation produced due to an irregularity of the external magnetic field, together with T2 relaxation by the impact between the spindles. T2* weighted images are very useful in clinical judgments which observe the degree of oxidation of the iron component due to a cerebral hemorrhage.
Such imaging techniques are useful to diagnose cerebrovascular diseases, which are second only to cancer as the ranking cause of death of Korean people, but there is a problem in that is necessary to go through for the acquisition process for each individual image. Diagnosis of acute stroke should be made promptly. This is because, the greater the time delay, the more exponentially brain cells undergo irreversible changes. Therefore, it is necessary to minimize the image acquisition time. If an acute stroke is suspected, imaging techniques that are undergone first are T2*GRE. If the blood brain condition can be judged by utilizing this imaging technique, the time taken to obtain TOF MRA can be shortened.